The relative vorticity of ocean surface winds from the QuikSCAT satellite
                        and its effects on the geneses of tropical cyclones in the South China
                        Sea

Fung

et al. 2008

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Ocean surface winds observed by the Quick Scatterometer (QuikSCAT) satellite prior to the geneses of 36 tropical cyclones (TCs) in the South China Sea (SCS) are investigated in this paper. The results show that there are areas with negative mean horizontal divergence around the TC genesis locations three days prior to TC formation. The divergence term [-(f+ζ)(∂u/∂x+∂v/∂y)] in the vorticity equation is calculated based upon the QuikSCAT ocean surface wind data. The calculated mean divergence term is about 10.3 times the mean relative vorticity increase rate around the TC genesis position one day prior to TC genesis, which shows the important contributions of the divergence term to the vorticity increase prior to TC formation. It is suggested that criteria related with the divergence and divergence term be applied in early detections of tropical cyclogenesis using the QuikSCAT satellite data.

Section: Discussionmentioning

confidence: 99%

Section: The Divergence and The Divergence Term Prior To The Geneses mentioning

confidence: 99%

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Features of ocean surface winds observed by the QuikSCAT satellite before tropical cyclogenesis over the South China Sea

Fung

et al. 2008

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“…Typhoon Durian (2001) was formed over the SCS, a large semi-enclosed marginal sea where TCs occur frequently (Chen and Ding, 1979;Wang et al, 2007a), and like many TCs in the SCS it was formed in the monsoon trough (Wang et al, 2007b), as a tropical depression west of Luzon at 0000 UTC 29 June (Fig.1). It moved northwestward and intensified into a tropical storm at 0000 UTC 30 June.…”

Section: Overview Of Typhoon Durian (2001)mentioning

confidence: 98%

Numerical simulation of the genesis of typhoon Durian (2001) over the South China Sea: The effect of sea surface temperature

Fung

2010

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Typhoon Durian (2001), which formed over the South China Sea (SCS), was simulated by using the Weather Research and Forecasting (WRF) model. The genesis of typhoon Durian which formed in the monsoon trough was reproduced by numerical simulations. The simulated results agree reasonably well with observations. Two numerical experiments in which the sea surface temperature (SST) was either decreased or increased were performed to investigate the impact of the SST on the genesis of the typhoon. When the SST was decreased by 5℃ uniformly for all grids in the model, the winds calculated became divergent in the lower troposphere and convergent in the upper troposphere, creating conditions in which the amount of total latent heat release (TLHR) was low and the tropical cyclone (TC) could not be formed. This simulation shows the importance of the convergence in the lower troposphere and the divergence in the upper troposphere for the genesis of the initial vortex. When the SST was increased by 1℃ uniformly for all grids, a stronger typhoon was generated in the results with an increase of about 10 m s -1 in the maximum surface wind speed. Only minor differences in intensity were noted during the first 54 h in the simulation with the warmer SST, but apparent differences in intensity occurred after 54 h when the vortex began to strengthen to typhoon strength. This experiment shows that warmer SST will speed the strengthening from tropical storm strength to typhoon strength and increase the maximum intensity reached, while only minor impact can be seen during the earlier stage of genesis before the TC reaches the tropical storm strength. The results suggest that the amount of TLHR may be the dominant factor in determining the formation and the intensification of the TC.

“…The non-developing and developing tropical disturbances are represented by asterisks and crosses respectively in the figure. Wang et al (2007a) found that genesis locations of tropical cyclones over the SCS are located in the northern SCS during the summer monsoon months (from May to September) and in the southern SCS during the winter monsoon months (from October to December), which could be explained by the mean background relative vorticity of ocean surface winds induced by the monsoon trough and coastal mountains. Similar to the distributions of genesis locations of tropical cyclones, the formation locations of tropical disturbances mainly concentrated in the northern SCS during the summer monsoon months and in the southern SCS during the winter monsoon months.…”

Section: Formation Locations Of Tropical Disturbancesmentioning

confidence: 97%

Statistical analysis of tropical disturbances over the South China Sea during 1997–2006

2011

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Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1997 to 2006, with 54 developing tropical disturbances which developed into tropical depressions and 104 non-developing tropical disturbances which never developed into tropical depressions. The development rate of tropical disturbances into tropical depressions was 34.18% in these ten years. During the period of this study, total annual numbers of tropical disturbances and developing tropical disturbances over the SCS had significant decreasing trends; however, the development rate of tropical disturbances had an insignificant increasing trend.